Amazon Dash Button Finds Your Phone

This scene replays quite often in our house: my wife has misplaced her cell phone so she asks me to call her. But where did I leave my cell phone? And the race is on! Who will find their phone first to call the other?

[Zapta] solves this problem with his Phone Finder. The system comes in two parts: a base station with WiFi that’s also connected to the house’s phone line, and an arbitrary number of Amazon Dash buttons that trigger dialing commands.

[Zapta] presses a Dash button, which connects over WiFi to the base station. The base station recognizes the MAC address of the button, looks up and dials the corresponding missing cell phone. This solves the need-a-phone-to-find-a-phone problem very neatly, and since Dash buttons are dirt cheap they can be scattered liberally around the house. They’re clearly marked “his” and “hers” suggesting a similar domestic dynamic.

If we were implementing the base station from scratch, we’d probably try to figure out how a single ESP8266 could do all of the heavy lifting, but browsing through [Zapta]’s GitHub and the included circuit diagram (PDF) demystifies the phone-line interface.

In the early days of cordless phones, we used to joke that a solution to losing them would be to attach a string and tie them to the wall. (Luddites!) We’re glad to see [Zapta] take this project in the opposite direction — using technological overkill to solve the unintended problems that arise from technological progress.

That’s an interesting idea. A high efficiency DC/DC that charges a 1C lion from few milliamps ~30V from the phone line such that the wifi can get the burst current for transmitting. May require a more power efficient CPU and Wifi stack.

Or you could just use a SIP line to ring the mobile and not need a land line. Write a script on the ESP to hang up within so many rings and there won’t be a cost.
Of course, you could also just write an app for the phone which’ll make it ring on demand. Such a thing probably already exists.

If you take the signal as being a particular MAC address coming onto your network, then all you need is any old device with network hardware, old tablet, old pda, old router, that you only turn on to send the bat signal, as long as you get it’s MAC right.

You can set your router to block traffic from the buttons to the outside world. This way your script is watching for the button to appear on the AP but you don’t actually need connectivity for them beyond that.

I have Zoiper installed on all the house mobile phones, and Asterisk on the ‘always on computer’ that runs the house services. It kind of helps at times if I lose my phone, but what I really want is something that tells me where my phone was just before its batteries died. If the battery gets down to 3%, I want a function that squawks its location in 3D space down to the nearest cubic meter to a central service.

.. and then a web page that draws a wireframe view of my current surroundings (house, office, shop) with my last known phone’s location glowing gently. If CSI can do it, why can’t I? Or perhaps a web page that says ‘warmer, warmer, cooler, cooler, warmer, hot, BOILING!’ as I move around. But then how would it know where I was, without some kind of geolocation, digital compass, GPS service .. oh, wait! My phone has all those .. ah.